Clofibrate and enzymatic induction in man.

The oral administration of clofibrate, 1 g per day for 13 days, did not modify the half-life of antipyrine and urinary glucaric acid excretion in five volunteers. Despite the fact that clofibrate is a strong inducer of hepatic microsomal enzymatic activity in the rat, in man it does not increase, at these doses, the metabolism of antipyrine and the urinary elimination of glucaric acid. Rifampicin, 600 mg per day orally for seven days, decreases the plasma steady-state concentrations of chlorophenoxyisobutyric acid, a major metabolite of clofibrate. It seems that the metabolism of clofibrate depends upon inducible enzymatic activity. When rifampicin and clofibrate are administered together, it may be important to increase the dose of clofibrate used.